1. Description of the Prior Art
The mass production of semiconductor devices is presently accomplished by production of a single crystalline wafer from which many individual semiconductive crystals are formed. One method presently employed to produce such devices is the formation of aligned V-grooves in the wafer containing the semiconductive crystals so that after further processing the semiconductive crystals can be separated by breaking the wafer along the V-grooves.
However, there are certain disadvantages in using this process, one of which is that in forming aligned grooves in a wafer containing semiconductive crystals, the wafer is held together only by the thinned crystal portions lying beneath the grooves making the wafers fragile and susceptible to cracking. In general, the prior art method for supporting and strengthening the wafer is to deposit polycrystalline intrinsic silicon (hereafter sometimes poly) on the grooved side only and thus passivate the junction. This one sided deposition usually causes strain and the wafer will crack even though the wafer will remain intact. However, after the poly is polish removed the wafer will crack during polishing or subsequent fabrication of a semiconductor chip. Under the prior art method, the thick poly layer is grown on the wafer at high temperatures. Frequently, the combination of high temperatures and one-sided coating would cause warpage if special precautions were not taken.
An example of this prior art form of passivation is shown in U.S. Pat. No. 3,806,771. According to the method described in this prior art, the groove is passivated by a thick glass bonding layer. However, it is important that the thermal coefficient of expansion of this bonding layer be no greater than that of the silicon. This is because if it were greater, since the layer is applied only to one side of the wafer, there would be stresses incurred which could cause warpage and cracking. Thus, a special bonding material, which is not readily available and is expensive, is required. In addition, it is a difficult and slow process to apply such a thick bonding layer directly to the surface of the groove, and the process is not readily adaptable to application of such a layer to both sides of the wafer.
Low pressure chemical vapor deposition has been used in the prior art to apply a very thin poly layer to the V-grooved side as a seed for growth of a thicker layer. However, no two-sided deposition has been used in this manner. This type of deposition is slow and has not been considered for application of a relatively thick (7.mu.) support layer.
As mentioned before, when the above method of one-sided reinforcement is used, with only one side of the wafer reinforced, the wafer would be under strain and would be unstable. This results in the breakage of virtually every wafer at some time during the processing and subsequent handling of the wafers. Thus, one-sided support has proved to be ineffective.